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Message-ID: <20250825195806.226328-1-zecheng@google.com>
Date: Mon, 25 Aug 2025 19:58:06 +0000
From: Zecheng Li <zecheng@...gle.com>
To: Peter Zijlstra <peterz@...radead.org>, Ingo Molnar <mingo@...hat.com>,
Arnaldo Carvalho de Melo <acme@...nel.org>, Namhyung Kim <namhyung@...nel.org>,
Mark Rutland <mark.rutland@....com>,
Alexander Shishkin <alexander.shishkin@...ux.intel.com>, Jiri Olsa <jolsa@...nel.org>,
Ian Rogers <irogers@...gle.com>, Adrian Hunter <adrian.hunter@...el.com>,
"Liang, Kan" <kan.liang@...ux.intel.com>, Masami Hiramatsu <mhiramat@...nel.org>
Cc: Xu Liu <xliuprof@...gle.com>, linux-perf-users@...r.kernel.org,
linux-kernel@...r.kernel.org, Zecheng Li <zecheng@...gle.com>
Subject: [PATCH v2 08/10] perf dwarf-aux: Skip check_variable for die_find_variable_by_reg
In die_find_variable_by_reg, match_var_offset already performs
sufficient checking and type matching. The additional check_variable
call is redundant, and its need_pointer logic is only a heuristic. Since
DWARF encodes accurate type information, which match_var_offset
verifies, skipping check_variable improves both coverage and accuracy.
This change implements
- Return type from die_find_variable_by_reg via a new `type` field in
find_var_data.
- In match_var_offset, use __die_get_real_type instead of
die_get_real_type to preserve typedefs. Move the (offset == 0) branch
after the is_pointer check to ensure the correct type is used, fixing
cases where an incorrect pointer type was chosen when the access
offset was 0.
- When comparing types from different scopes, first compare their type
offsets. A larger offset means the field belongs to an outer
(enclosing) struct. This helps resolve cases where a pointer is found
in an inner scope, but a struct containing that pointer exists in an
outer scope. Previously, is_better_type would prefer the pointer type,
but the struct type is actually more complete and should be chosen.
Signed-off-by: Zecheng Li <zecheng@...gle.com>
---
tools/perf/util/annotate-data.c | 12 ++++++++----
tools/perf/util/dwarf-aux.c | 30 +++++++++++++++++-------------
tools/perf/util/dwarf-aux.h | 2 +-
3 files changed, 26 insertions(+), 18 deletions(-)
diff --git a/tools/perf/util/annotate-data.c b/tools/perf/util/annotate-data.c
index e067e91f2037..b1a4b02afeb1 100644
--- a/tools/perf/util/annotate-data.c
+++ b/tools/perf/util/annotate-data.c
@@ -1551,19 +1551,21 @@ static int find_data_type_die(struct data_loc_info *dloc, Dwarf_Die *type_die)
if (!die_find_variable_by_addr(&scopes[i], dloc->var_addr,
&var_die, &type_offset))
continue;
+ /* Found a variable, see if it's correct */
+ result = check_variable(dloc, &var_die, &mem_die, reg,
+ type_offset, is_fbreg);
} else {
/* Look up variables/parameters in this scope */
if (!die_find_variable_by_reg(&scopes[i], pc, reg,
- &type_offset, is_fbreg, &var_die))
+ &mem_die, &type_offset, is_fbreg, &var_die))
continue;
+ result = PERF_TMR_OK;
}
pr_debug_dtp("found \"%s\" (die: %#lx) in scope=%d/%d (die: %#lx) ",
dwarf_diename(&var_die), (long)dwarf_dieoffset(&var_die),
i+1, nr_scopes, (long)dwarf_dieoffset(&scopes[i]));
- /* Found a variable, see if it's correct */
- result = check_variable(dloc, &var_die, &mem_die, reg, type_offset, is_fbreg);
if (result == PERF_TMR_OK) {
if (reg == DWARF_REG_PC) {
pr_debug_dtp("addr=%#"PRIx64" type_offset=%#x\n",
@@ -1575,7 +1577,9 @@ static int find_data_type_die(struct data_loc_info *dloc, Dwarf_Die *type_die)
pr_debug_dtp("type_offset=%#x\n", type_offset);
}
- if (!found || is_better_type(type_die, &mem_die)) {
+ if (!found || dloc->type_offset < type_offset ||
+ (dloc->type_offset == type_offset &&
+ is_better_type(type_die, &mem_die))) {
*type_die = mem_die;
dloc->type_offset = type_offset;
found = true;
diff --git a/tools/perf/util/dwarf-aux.c b/tools/perf/util/dwarf-aux.c
index 6e8877ff2172..56e1b5690dc4 100644
--- a/tools/perf/util/dwarf-aux.c
+++ b/tools/perf/util/dwarf-aux.c
@@ -1378,6 +1378,8 @@ struct find_var_data {
Dwarf_Addr addr;
/* Target register */
unsigned reg;
+ /* Access data type */
+ Dwarf_Die type;
/* Access offset, set for global data */
int offset;
/* True if the current register is the frame base */
@@ -1390,29 +1392,28 @@ struct find_var_data {
static bool match_var_offset(Dwarf_Die *die_mem, struct find_var_data *data,
s64 addr_offset, s64 addr_type, bool is_pointer)
{
- Dwarf_Die type_die;
Dwarf_Word size;
s64 offset = addr_offset - addr_type;
- if (offset == 0) {
- /* Update offset relative to the start of the variable */
- data->offset = 0;
- return true;
- }
-
if (offset < 0)
return false;
- if (die_get_real_type(die_mem, &type_die) == NULL)
+ if (__die_get_real_type(die_mem, &data->type) == NULL)
return false;
- if (is_pointer && dwarf_tag(&type_die) == DW_TAG_pointer_type) {
+ if (is_pointer && dwarf_tag(&data->type) == DW_TAG_pointer_type) {
/* Get the target type of the pointer */
- if (die_get_real_type(&type_die, &type_die) == NULL)
+ if (__die_get_real_type(&data->type, &data->type) == NULL)
return false;
}
- if (dwarf_aggregate_size(&type_die, &size) < 0)
+ if (offset == 0) {
+ /* Update offset relative to the start of the variable */
+ data->offset = 0;
+ return true;
+ }
+
+ if (dwarf_aggregate_size(&data->type, &size) < 0)
return false;
if ((u64)offset >= size)
@@ -1529,7 +1530,7 @@ static int __die_find_var_reg_cb(Dwarf_Die *die_mem, void *arg)
* when the variable is in the stack.
*/
Dwarf_Die *die_find_variable_by_reg(Dwarf_Die *sc_die, Dwarf_Addr pc, int reg,
- int *poffset, bool is_fbreg,
+ Dwarf_Die *type_die, int *poffset, bool is_fbreg,
Dwarf_Die *die_mem)
{
struct find_var_data data = {
@@ -1541,8 +1542,11 @@ Dwarf_Die *die_find_variable_by_reg(Dwarf_Die *sc_die, Dwarf_Addr pc, int reg,
Dwarf_Die *result;
result = die_find_child(sc_die, __die_find_var_reg_cb, &data, die_mem);
- if (result)
+ if (result) {
*poffset = data.offset;
+ *type_die = data.type;
+ }
+
return result;
}
diff --git a/tools/perf/util/dwarf-aux.h b/tools/perf/util/dwarf-aux.h
index f20319eb97a9..beb6926aaa71 100644
--- a/tools/perf/util/dwarf-aux.h
+++ b/tools/perf/util/dwarf-aux.h
@@ -167,7 +167,7 @@ int die_get_var_range(Dwarf_Die *sp_die, Dwarf_Die *vr_die, struct strbuf *buf);
/* Find a variable saved in the 'reg' at given address */
Dwarf_Die *die_find_variable_by_reg(Dwarf_Die *sc_die, Dwarf_Addr pc, int reg,
- int *poffset, bool is_fbreg,
+ Dwarf_Die *type_die, int *poffset, bool is_fbreg,
Dwarf_Die *die_mem);
/* Find a (global) variable located in the 'addr' */
--
2.51.0.261.g7ce5a0a67e-goog
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